Contact with arc propelling means embodied therein

ABSTRACT

In a vacuum type circuit interrupter having a pair of relatively movable contacts, each contact comprises a contact stud to which a relatively wider copper contact body or disk is attached. Magnetically permeable, highly resistive arc propelling means are embedded in the contact body. These means comprise a circular center portion of the same or larger diameter as the contact stud and from which (or from near which) a plurality of spirally shaped arms or vanes radiate towards the periphery of the contact. The arc propelling means create a looped current path in the contact body during contact closed position to intensify outwardly radiating magnetic forces upon contact opening to improve arc rotation thereby aiding in arc extinguishment.

United States Paten H9] Dethlefsen CONTACT WITH ARC PROPELLING MEANS EMBODIED THEREIN [75] Inventor: Roll Dethlefsen, New Berlin, Wis.

[73] Assignee: Allis-Chalmers Manufacturing Company, Milwaukee, Wis.

[22] Filed: Feb. 16, 1971 [21] Appl.No.: 115,594

[56] References Cited UNITED STATES PATENTS 10/ l966 Ranheim ..200/l44 B 6/l967 Pflanz ....200/l44 B 1/1968 Smith, Jr.... ....200/l44 B 8/1969 Sofianek ..200/l44 B 1 Jan. 16, 1973 Primary Examiner-Robert S. Macon Attorney-Thomas F. Kirby, Robert B. Benson and Lee H. Kaiser [57] ABSTRACT In a vacuum type circuit interrupter having a pair of relatively movable contacts, each contact comprises a contact stud to which a relatively wider copper contact body or disk is attached. Magnetically permeable, highly resistive arc propelling means are embedded in the contact body. These means comprise a circular center portion of the same or larger diameter as the contact stud and from which (or from near which) a plurality of spirally shaped arms or vanes radiate towards the periphery of the contact. The are propelling means create a looped current path in the contact body during contact closed position to intensify outwardly radiating magnetic forces upon contact opening to improve arc rotation thereby aiding in arc extinguishment.

5 Claims, 7 Drawing Figures CONTACT WITH ARC PROPELLING MEANS EMBODIED THEREIN BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates generally to means for extinguishing electric arcs generated between separable contacts. More specifically, it relates to arc propulsion means which are embodied in contact structures.

2. Description of the Prior Art It is known that the arc interrupting capacity of a pair of relatively movable vacuum type circuit breaker contacts can be increased substantially by propelling the arc terminals at high speed across the contact surfaces. U.S. Pat. No. 3,327,081 issued June 20, 1967 to Herbert M. Pflanz for Contact with High Resistance Material Insert discloses contacts utilizing this general principle and shows a disk-type contact having one or more spiral slots therein which are filled with high resistant material such as iron or nickel to facilitate arc extinguishment. While these contacts and other fully slotted type contacts are satisfactory for their intended purpose, fully slotted contacts tend to be mechanically weak and present interrupted contact surfaces to the arc terminals traveling there-across.

SUMMARY OF THE INVENTION In accordance with the invention, there is provided an improved electrical contact, particularly well adapted for use in high power vacuum type electric circuit interrupters, which comprises a disk-like body of highly conductive material, such as pure copper, and which is attached to a contact rod of smaller diameter than the disk like body. Metallic arc directing means of high magnetic permeability and high electrical resistivity, preferably iron or nickel, are embedded or incased in the contact body. In one embodiment the arc directing means comprise a centrally located section (of the same or larger diameter as the diameter of the contact rod) from which one or more integrally formed spirally shaped arms or vanes radiate toward the periphery of the contact body. In another embodiment the arc directing means comprise a centrally located section (of the same or larger diameter as the diameter of the contact rod) and spirally shaped arms or vanes. The inner ends of the arms or vanes of the other embodiment are adjacent and maybe attached to the central section and radiate outwardly therefrom toward the periphery of the contact. If preferred, the outer ends of the arms of either embodiment may be joined together by a ring. Also, if preferred, all embodiments may comprise suitable means, such as a partially embedded copper-bismuth alloy insert on the contact face, which have antiwelding properties.

OBJECTS tact surface is presented to the arc terminals moving thereacross.

Another object is to provide such contacts which are constructed so that skin effect and internal resistance will influence current distribution within the contact and improve magnetic force distribution thereby enhancing arc movement and are extinguishment.

Another object is to provide improved contacts of the aforesaid character which have high current interrupting capability, which are mechanically strong, which are reliable in use, and which are relatively easy and less costly to manufacture.

Another object is to provide improved contacts wherein the magnetic field at the surface of the contact is focused and intensified by means embedded or incased therein, thereby providing more rapid arc movement or rotation, decreased melting of contact materials, and increased interrupting capability in circuit interrupters using such contacts.

Other objects and advantages of the invention will hereinafter appear.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawing illustrates several preferred embodiments of the invention but it is to be understood that the embodiments illustrated are susceptible of modifications with respect to details thereof without departing from the scope of the appended claims.

In the drawing:

FIG. 1 is a view partially in vertical section and partially in elevation of a vacuum type circuit interrupter employing contacts in accordance with a first embodiment of the present invention;

FIG. 2 is an enlarged fragmentary view in vertical section taken through one of the contacts shown in FIG. 1, a pair of arms associated with the arc directing means being depicted;

FIG. 3 is a sectional view taken along the line III-III of FIG. 2, showing the configuration of the arc directing means the the arms associated therewith in plan;

FIG. 4 is a view similar to FIG. 2 ofa contact in accordance with a second embodiment of the invention;

FIG. 5 is a sectional view taken along the line V-V of FIG. 4, with the configuration of the arc directing means and the associated arms being depicted in plan;

FIG. 6 is a partial sectional view taken along the line VI--VI of FIG. 3; and

FIG. 7 is a partial sectional view taken along the line VlIVll of FIG. 5.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, the numeral 10 designates a vacuum type electric circuit interrupter or switch employing relatively movable contacts incorporating the present invention. Vacuum switch 10 comprises a cylindrical envelope 12 which may be formed, for example, of a suitable insulating material such as glass or ceramic. One end of envelope 12 is provided with an annular rim 14 to which is rigidly secured in a vacuum tight connection one end of a metal ring or flange 16. A circular metallic end cap 18 is sealed along its peripheral edge to the other end of flange l6. Cap 18 supports a stationary contact rod or support 20 which extends along the longitudinal axis of envelope l2 and is rigidly supported so as to be restricted against longitudinal or lateral movement. The opposite end of envelope 12 is provided with an annular rim 22 to which is rigidly secured in a vacuum tight connection one end of a ring or flange 24. A toroidally shaped retainer 26 is sealed along its peripheral edge in a vacuum tight connection to flange 24. A metallic cylindrically shaped flexible bellows 28 is rigidly secured in a vacuum tight connection at one end thereof to retainer 26. The other end of bellows 28 surrounds and is rigidly secured in a vacuum tight connection to a movable contact rod or support 30 which is arranged to extend through retainer 26 into envelope l2 and is in cooperating relationship with contact support 20.

The relatively movable contact rods or supports and are made of a suitable electrically conductive material, such as copper or the like and preferably are cylindrical in form. Contact support 30 is understood to be arranged for longitudinal movement along its axis for a limited predetermined distance by a suitable contact actuating mechanism (not shown).

The contact rods or supports 20 and 30 support contacts 32 and 34, respectively, hereinafter described. In order to control the dispersion of arcing products emitted upon separation of the contacts 32 and 34, a cylindrical cup shaped tube or shield is provided which is rigidly secured to contact rod or support 20 and is arranged to extend beyond the adjacent ends of both contact supports 20 and 30 so as to surround the contacts 32 and 34 when the contacts are engaged and disengaged. Shield 35 may be formed of glass or any suitable metallic or non-metallic, heat resistant material.

Upon actuation of movable contact rod or support 30 in axial contact engaging or contact disengaging direction, bellows 38 deflects, allowing restricted longitudinal movement of contact 34. The required range of movement of contact 34 is very small. For example, with only three-'sixteenths of an inch separation between engaging surfaces of contacts 32 and 34 a current of many thousand amperes at an AC voltage of 18,000V can be safely interrupted. The contacts when engaged can continuously conduct current of several hundred amperes.

Referring to FIG. 1, contacts 32 and 34 are shown as substantially identical to each other and a description of contact 34 will suffice for contact 32 as well. However, it is to be understood that the invention can be embodied in a circuit interrupter'or other are extinguishing electrical device wherein only one contact or terminal is constructed in accordance with the present invention.

Contact 34 comprises a body 36 of highly conductive material such as copper in the form ofa disk which is of substantially greater diameter than its associated contact rod 30. Are directing means 38 having high magnetic permeability and high electrical resistivity as compared to the contact body, and comprising, for example, iron or nickel, are embedded in body 36 as by being cast therein. In the embodiment shown in FIGS. 1, 2 and 3, are directing means 38 comprises a thin,

flat, substantially circular centrally located section 40,

having one or more spirally arranged arms or vanes 42 which are attached to the central section 40 at their inner root ends 44. As best shown in FIG. 3, the arms 42 radiate in a spiral outwardly toward the periphery of contact 34 with the outer ends thereof disposed so as not to intersect the peripheral surface of the contact. The diameter of central section 40 of the arc directing means 38 is in the order of the diameter of contact rod 30. Are directing means 38 may be fabricated in one piece as by punching, stamping or cutting from sheet metal or could be fabricated by welding flat, rectangular, undivided arms 42 to central section 40. As depicted in FIGS. 2 and 3 the arc directing means 38 is fabricated in one piece as being cut from sheet metal stock of suitable thickness. The arms or vanes 42 are twisted at the root area 44 so that the surfaces thereof are displaced with respect to the surface of the central section 40 of the arc directing means. The arms are also formed bent into a curvalinear or spiral shape, as depicted in FIG. 3. Preferably, contact 34 further comprises an insert 46 on the face thereof for contact-making purposes which has antiwelding properties and comprises, for example, copper-bismuth alloy or other suitable material.

A contact such as contact 34 operates as follows. When contacts 32 and 34 are closed as shown in FIG. 2, electric current flows from contact rod 30, through contact 34, through contact 32, to contact rod-20. Current flow follows the path indicated by the dotted lines 48 in FIG. 2 because the central section 40 of arc directing means 38 presents a higher electrical resistance to current flow than body 36 of contact 34. Thus, in the contact closed condition, the current flow path forms a loop in body 36 and generates a magnetic force field which radiates outwardly from the center of contact 34 toward its periphery. When contacts 32 and 34 separate, arcing is initiated between insert 46 of contact 34 and the corresponding insert of contact 32. However, the offset or looped current flow indicated by the dotted lines 48 is already generating magnetic forces which drive the arc and are terminals off of and radially away from insert 46 and toward the periphery of contact 34, as indicated by the dotted lines 49 in FIG. 1. The reason for this are motion is the tendency of current loop 48 to expand outwardly and enlarge itself along the lines 49 in high current type devices wherein the arc moves in an amperian (nonretrograde) direction. Once the arc leaves the central area of contact body 36, a circumferential current distribution is established by arc directing means 38. In particular, as FIG. 6 shows, the spiral arms or vanes 42, because of their electrical resistance and magnetic properties, direct current flow through body 36 so that a magnetic force field is generated which will impart a circumferential or rotational component to the arc and intensify the magnetic field generated by current flow through the spiral structure. The vanes 42 focus the magnetic field associated with current flow through the copper between the vanes thereby increasing magnetic field strength in the region between the spaced apart contacts 32 and 34 where it effects acceleration of the arc. The total effect aforedescribed is desirable in order to limit erosion of the region of contact 34 which mechanically engages contact 32, i.e., the insert 46 in the embodiment shown. Furthermore, higher are cur- I rents are possible if the arc terminals are driven into the surface of pure copper body 36, rather than remaining on alloy insert 46.

It should be noted that the higher conductivity of body 36 and the difference in the skin effect inherent in arc directing means 38 and the contact body 36 enforces a current distribution pattern in contact 34 which largely follows the spiral shape of arms 42. Since the skin effect depth at 60 Hertz for copper body 36 is about millimeters and for are directing means 38 is about 1 millimeter, the thickness of arms 42 should be about 1 millimeter. Furthermore, since the magnetic field associated with the distribution of rotating current must penetrate the layer of copper in body 36 covering the arc directing means 38, the copper layer should be as thin as possible consistent with possible erosion of the surfaces. In practice, a thickness of about 2 millimeters is desirable over most of contact 34. However, since most erosion is likely to occur near the periphery of contact 34, a thicker layer of copper may be provided in this region if desired. Also, the copper layer may be corrugated azimuthally as at 72 to provide the contact body with a greater amount of material on the upper skin layer in order to optimize the magnetic field penetration relative to the tolerable metal erosion due to arc exposure.

In FIGS. 4 and 5, the numeral 50 designates another type of contact in accordance with the invention which could be employed in circuit interrupter 10 instead of the contacts 32 and 34. Contact 50 comprises a diskshaped body 52 of highly conductive material, such as copper which is of greater diameter than contact rod 30. Arc directing means 54 of the same material as arc directing means 38, hereinbefore described, is embedded in body 52 and comprise two descrete portions or assemblies, namely, a thin, flat, substantially circular, centrally located section 56 and an outer section 58 comprising one or more radially arranged spiral arms or vanes 60 and a circular ring 62. As depicted in FIG. 4, the central section 56 is of the same diameter as the diameter of contact rod 30 but may be of a larger diameter if desired. The function of section 56 can also be fulfilled by a suitably shaped void instead ofa metallic insert. The inner ends 64 of the arms 60 are adjacent but are not necessarily connected to center section 56. The outer ends of the arms 60 can be connected to the ring 62. Contact 50 preferably comprises an insert 64' similar to insert 46, hereinbefore described. Manufacturing of the contact 50, FIGS. 4 and 5, is facilitated by the vanes 60 being welded in spaced relationship to the surface of the plate 70. The outer ends of the vanes 60 are then welded to the inner peripheral surface of the ring 52. The upper inner corners of the inner ends 64 of the vanes 60 are welded to the periphery of the center section 56. With the arc directing means 58 thus assembled the copper body 52 is casted about the are directing means 58 to form a unitary contact. A bottom axial bore is formed in the contact 50 to receive the end of the contact rod 30 and the contact brazed to the rod. A suitable axial bore is also formed in the top surface of the contact to receive the insert 64 which is secured therein by brazing. In operation, current flow in contact 50 in closed circuit condition is indicated by the lines 68 shown in FIG. 4. ln open circuit condition, current flow is similar to that shown by the lines 49 in FIG. 1 in connection with contact 34. In contact 50, the

closed magnetic path provided by the vanes and bottom plate 70 intensifies the ma netic field which is intensi ted in the space between e contacts and results in accelerated movement of an arc across the arc surface contact.

It will be apparent from the foregoing that contacts in accordance with the present invention have intensified and directional magnetic forces at the surface thereof which result in rapid arc movement and rota tion, decreased melting of contact materials, and increased arc interrupting capability of the contacts and circuit interrupters using such contacts. Furthermore, the arc terminals travel on a smooth, continuous, unbroken surface of high purity copper and are not confronted with gaps or dissimilar materials which tend to promote undesirable rooting of an arc, with consequent vaporization and contact deterioration.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. Electrical contact means for a vacuum circuit interrupter comprising; contact rod means; an electrical contact body of highly conductive material mounted on said contact rod means and having a diameter that is greater than the diameter of the adjacent portion of said contact rod means;

current directing and are propelling means having greater electrical resistance and higher magnetic permeability than said contact body and completely incased within said contact body to thereby present an uninterrupted contact surface to an arc moving across the surface, said are propelling means including a solid circular central portion axially aligned relative to said contact rod means and having a diameter at least equal to the diameter of the adjacent portion of said contact rod means to create a loop current path around said central portion, said are propelling means further including at least one vane radiating outwardly in a spiral path from the peripheral edge of said central portion towards the periphery of said contact body to impart a circumferential or rotational component to the arc, said vane being also completely incased in said contact body.

2. An electrical contact according to claim 1 wherein said are propelling means includes a plurality of vanes completely incased in said contact body, each of said vanes radiating outwardly in a spiral path from the solid circular central portion towards the periphery of said contact body to a point short thereof.

3. An electrical contact according to claim 2 wherein said arc propelling vanes are completely incased in said contact body approximately two millimeters below the are surface of said contact body.

4. An electrical contact according to claim 3 wherein said are propelling vanes have a thickness dimension of substantial one millimeter.

5. An electrical contact according to claim 3 wherein the are surface of said contact body is corrugated azimuthally, whereby the magnetic field penetration relative to the tolerable metal erosion of the arcing surface due to are exposure is optimized.

* III 

1. Electrical contact means for a vacuum circuit interrupter comprising; contact rod means; an electrical contact body of highly conductive material mounted on said contact rod means and having a diameter that is greater than the diameter of the adjacent portion of said contact rod means; current directing and arc propelling means having greater electrical resistance and higher magnetic permeability than said contact body and completely incased within said contact body to thereby present an uninterrupted contact surface to an arc moving across the surface, said arc propelling means including a solid circular central portion axially aligned relative to said contact rod means and having a diameter at least equal to the diameter of the adjacent portion of said contact rod means to create a loop current path around said central portion, said arc propelling means further including at least one vane radiating outwardly in a spiral path from the peripheral edge of said central portion towards the periphery of said contact body to impart a circumferential or rotational component to the arc, said vane being also completely incased in said contact body.
 2. An electrical contact according to claim 1 wherein said arc propelling means includes a plurality of vanes completely incased in said contact body, each of said vanes radiating outwardly in a spiral path from the solid circulAr central portion towards the periphery of said contact body to a point short thereof.
 3. An electrical contact according to claim 2 wherein said arc propelling vanes are completely incased in said contact body approximately two millimeters below the arc surface of said contact body.
 4. An electrical contact according to claim 3 wherein said arc propelling vanes have a thickness dimension of substantial one millimeter.
 5. An electrical contact according to claim 3 wherein the arc surface of said contact body is corrugated azimuthally, whereby the magnetic field penetration relative to the tolerable metal erosion of the arcing surface due to arc exposure is optimized. 